Engine Fuel Metering Systems Flashcards
7 cards from real AMT practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Engine Fuel Metering Systems flashcards as text
In a bendix-type RSA fuel injection system, what component ensures no fuel flows to the cylinders when the engine is shut down?
Answer: Spring-loaded flow divider that closes when pressure drops
The spring-loaded flow divider closes when fuel pressure drops below a set value (e.g., at shutdown), preventing fuel seeping into cylinders and causing hydraulic lock.
What is the purpose of a vapor return line on an engine-driven fuel pump?
Answer: To route fuel vapors back to the tank to prevent vapor lock and maintain liquid fuel delivery
The vapor return line allows fuel vapor and hot fuel to be routed back to the tank, ensuring the pump delivers only liquid fuel to the carburetor or injector.
A lean mixture at idle speed in a float carburetor is MOST likely caused by:
Answer: A blocked or maladjusted idle air bleed
The idle air bleed introduces air into the idle fuel circuit to atomize fuel; if blocked, too much air can still enter through air leaks, but if the bleed is too open or the idle jet is too small, the mixture leans.
When inspecting a fuel injection nozzle, you find a partially clogged screen. The correct maintenance action is to:
Answer: Clean the screen using approved solvent and dry compressed air, then reinstall and recheck flow
Approved maintenance for clogged injector screens is to clean with solvent and dry air; do not alter orifice sizes as this upsets calibrated flow balance.
What is the function of a boost pump in relation to the main engine-driven fuel pump?
Answer: It provides fuel pressure for engine starting and serves as a backup if the engine-driven pump fails
The electric boost pump ensures adequate fuel pressure during starting (before the engine-driven pump is up to speed) and provides backup pressure if the engine-driven pump fails.
In a turbocharged engine with a fuel injection system, the fuel control unit references what pressure to compensate for boost?
Answer: Absolute pressure (MAP) downstream of the turbocharger compressor
The fuel control unit references manifold absolute pressure (boosted air pressure) to meter fuel proportional to the denser, boosted air entering the engine.
Which of the following best describes the role of the idle jet in a float carburetor?
Answer: It provides the primary fuel metering circuit during low-throttle, low-airflow operation
At low throttle settings, airflow through the main venturi is insufficient to draw fuel through the main jet, so the idle jet circuit provides the metered fuel flow.